Image forming method and apparatus with toner recycling unit

ABSTRACT

A method and apparatus for electrophotographic image forming are provided incorporating an improved toner recycling unit. This recycling unit is devised such that the selectable switching between toner recycling and non-recycling modes be continually carried out according to the decision based on the present amount of paper dusts measured by a paper dust measuring unit provided in a paper dust removal unit. The image forming apparatus incorporating the toner recycling unit is therefore capable of efficiently recycling the toner recovered from a cleaning unit without removing contaminants such as paper dusts and toner aggregates included in the recycled toner, thereby preventing the emergence of undesirable picture image anomalies such as whisker images and black dots.

BACKGROUND

1. Field

This patent specification relates generally to an image forming methodand apparatus with toner recycling unit, and more specifically to themethod and apparatus provided with improved toner recycling capabilityby means of selectively switching between recycling and non-recyclingmodes based on the results from toner measurements in recycled toner.

2. Discussion of the Background

The electrophotographic image forming process is well known. In imageforming apparatuses such as a copying machine, printer and facsimileapparatus, in general, the formation of the images is carried outthrough the electrophotographic steps of forming electrostatic latentimages on an image bearing member, developing as visible toner imagesusing toner particles, and transferring the toner images by a transfermeans onto a copy sheet, which subsequently passes through a fixing unitto form fixed images on the sheet.

Following transfer of the toner images onto the copy sheets, residualdeveloping material remaining on the image bearing member (orphotoreceptor drum) is generally removed by a cleaning device such as,for example, cleaning blade, and subsequently collected in a containertank for containing recovered toner material.

During the formation of images on the image bearing member such asphotoreceptor drum and also toner transfer onto a copy sheet by means ofthe transfer means, residual toner will generally result onto the imagebearing member primarily for the following reasons: The rate of tonertransfer during transfer steps is not able to reach 100% and thebackground density between images can not be zero, either.

The residual toner, therefore, results in the dirty background incontrast to produced images on copy sheets. As mentioned above, theresidual toner is subsequently collected in a container tank to bediscarded afterward.

With increasing concern for resources and operation costs in recentyears, recycling of the used toner material has been devised. Forexample, there disclosed in Japanese Laid-Open Patent Application No.6-175488 is that used toner is collected and returned by a tonertransporting unit to several units such as developing unit and tonersupplying unit to be admixed with fresh toner material, and issubsequently reused for forming toner images on the image bearingmember. The recent trend for toner recycling continue to increase inconventional image forming apparatuses.

In addition, it may be noted that the ratio of the amount of residualtoner material to the total amount thereof generally used inconventional image forming apparatuses ranges approximately from 15% to25%.

Several foreign materials or contaminants, which are exemplified bypaper dusts and toner aggregates with its size larger than the desirablesize, are often included in recycled toner in no small numbers. Thesematerials may be utilized repeatedly during the recycling process in thetoner recycling unit incorporated in image forming apparatus. As aresult, several drawbacks are encountered in the image forming using therecycling unit, which are known as picture image anomalies such as blankspots and dark dots.

Although there provided in the aforementioned disclosure is a filterunit for removing paper dusts and toner aggregates, satisfactory devicesand techniques therefor are yet to be devised.

As one of the above-mentioned picture image anomalies, whisker imagesare cited, which are formed being whisker-shaped against whitebackground on a copy sheet, as illustrated in FIG. 13.

The whisker images are considered to be caused by paper dusts. Namely,the paper dusts are first originated from copy sheets, contained inrecycled portion of the toner, and transported to the image bearingmember when recycled. Along the recycling steps, therefore, theconcentration of the paper dusts steadily increases in recycled tonercomponent in the recycling path.

During subsequent developing step with toner particles, toner particlesare adhered to the paper dusts, and then displaced altogether onto theimage bearing member. As a result, the thus formed paper dustsaccompanied by toner particles are subsequently transferred onto a copysheet during the transfer step, then emerge as the whisker imagesespecially visible against white background of the copy sheet.

It is noted that the steady increase in the content of paper dusts inrecycled toner is considered due to the fact that the portion of thepaper dusts, which is previously formed in the developing unit andincluded in the recycled toner, is generally removed by a copy sheet, tothereby return to the developer along the recycling, and this portion isadded to that of paper dusts originated now from newly fed copy sheets.

In case when a transfer unit is used incorporating another device suchas transfer belt or roller, residual toner is also formed in thesedevices. However, this portion of residual toner is not recycled inpractice, since the amount thereof is small and its quality isrelatively poor because of a larger content of paper dusts than thatremaining on the image bearing member.

In addition, the present inventors investigated in detail on thegeneration of paper dusts by experimentation. They have found the amountof paper dusts, which is transported to the image bearing member by eachcopy sheet, varies considerably depending on the kind, or the quality ofcopy sheet.

For example, paper dusts are rarely found in the residual toner for copysheets of fine quality even after feeding 300 k (i.e., 300 thousand)copy sheets, which is in contrast with a larger amount of the paperdusts for recycled or ordinary papers, in that more than 50 whiskerimages are sometimes recognized on an A4 size sheet after 300 k copysheets.

In order to alleviate such difficulties, an appropriate device such as,for example, a classifier may preferably be provided for removingaggregated toner particles and paper dusts. This is exemplified by amesh mounted in a toner recycling path, in which toner particles thatpass through the mesh are put into a recycled use, while those left outare discarded. In such a classifier, however, difficulties still persistsuch as in clogging by the particles, durability of the mesh, andthorough removal of residual particle or dusts on the mesh. Therefore,improvements are yet to be made on this technique as well.

In known image forming apparatuses incorporating toner recycling units,therefore, several difficulties are encountered of appropriatelyremoving undesirable contaminants to thereby prevent picture imageanomalies such as whisker images and dark dots, as mentioned earlier.

In addition, since the amount of paper dusts and toner aggregates, whichare included in the recycled toner, varies considerably depending on thekind of copy sheet and of toner in use as also indicated above, anothermethod may be devised, in which the amount of the toner to be recycledout of the recovered toner is suitably adjusted depending on theabove-mentioned amount of the contaminants which is presently obtained.That is, the ratio of the amount of recycled toner to that of recoveredtoner, or toner recycling rate, is adjusted so as to prevent pictureanomalies.

However, since the amount of contaminants further varies depending ontemperature and humidity as well, precise estimation and subsequentadjustments of the toner recycling rate has remained quite difficult inpractice. This difficulty may therefore cause another problem, in thatsome of recovered toner may be wastefully discarded when the recyclingsystem is operated with unduly low toner recycling rate.

SUMMARY

Accordingly, it is an object of the present disclosure to provide animage forming apparatus provided with an improved toner recycling unit,having most, if not all, of the advantages and features of similaremployed units, while eliminating many of their disadvantages.

It is another object of the present disclosure to provide a tonerrecycling unit in the image forming apparatus capable of efficientlyrecycling the toner recovered from a cleaning unit, which is devisedsuch that the selectable switching between the toner recycling andnon-recycling modes be continually carried out according to the decisionbased on the present amount of paper dusts, thereby preventing theemergence of undesirable picture image anomalies.

The following brief description is a synopsis of only selected featuresand attributes of the present disclosure. A more complete descriptionthereof is found below in the section entitled “Description of thePreferred Embodiments”

An image forming method is disclosed herein including at least the stepsof forming an electrostatic latent image on an image bearing member,forming a toner image by developing the latent image using toner on theimage bearing member, transferring the toner image to a substrate, andrecovering the toner material remaining on the image bearing memberfollowing the transfer.

This image forming method is characterized by including the followingadditional steps such as

computing an acceptable number of count of copy sheets that can beutilized in image forming in the forthcoming series of copying stepsuntil immediately before the threshold for the emergence of pictureimage anomalies caused by contaminants in the toner in the tonerrecycling unit, based on a prescribed number of count of copy sheetsthat is experimentally obtained in advance, under a variety of mutuallyindependent conditions, as the number of count of copy sheets that canbe utilized in image forming for the period of time from the start ofthe recycled use of the toner until immediately before the threshold forthe emergence of picture image anomalies caused by contaminants in thetoner in the toner recycling unit, and on a cumulative sheet count whichis accumulated in the present series of copying steps under runningconditions as the number of count of copy sheets that is accumulated inthe present series of copying steps after starting the recycled use ofthe toner, in which,

if the acceptable number of count of copy sheets is equal to, or greaterthan an anticipated number of count of copy sheets that can be utilizedin image forming in the forthcoming series of copying steps, theforthcoming series of copying steps are carried out in the tonerrecycling mode,

while the acceptable number of count of copy sheets is less than ananticipated number of count of copy sheets that can be utilized in imageforming in the forthcoming series of copying steps, the forthcomingseries of copying steps are carried out in the toner non-recycling mode.

In addition, at the instant when the acceptable number of count of copysheets is exceeded by the anticipated number of count of copy sheets, atoner discarding mode is implemented, in which all of the toner, that isrecovered by the cleaning unit to be recycled into the developing unit,is discarded to a toner discarding tank.

Accordingly, it becomes feasible with the present method of imageforming for the toner recovered by the cleaning unit be efficientlyrecycled without removing contaminants such as aggregated tonerparticles and paper dusts included in the recycled toner.

In addition, since contaminants of the amount unduly large, which maycause whisker images, can be excluded from the toner recycling path, theoccurrence of undesirable picture image anomalies can be prevented.

According to another aspect, an image forming apparatus is disclosedincluding at least an image bearing member, an exposure unit for formingan electrostatic latent image on the image bearing member, a developingunit for forming a toner image by developing the latent image usingtoner on the image bearing member, a transfer unit for transferring thetoner image to a substrate, a cleaning unit for cleaning the imagebearing member by removing the toner material remaining on the imagebearing member following the transfer, and a toner recycling unit forreturning the toner removed from the image bearing member to thedeveloping unit.

This image forming apparatus is characterized by including the followingadditional units such as

a prescribed sheet count memory for storing a prescribed number of countof copy sheets that is experimentally obtained as the count that can beutilized in image forming for the period of time from the start of therecycled use of the toner until immediately before the threshold for theemergence of picture image anomalies caused by contaminants in the tonerin the toner recycling unit,

a cumulative sheet count memory for storing a cumulative number of countof copy sheets that is accumulated in the present series of copyingsteps after starting the recycled use of said toner,

a computing unit for computing an acceptable number of count of copysheets that can be utilized in image forming in the forthcoming seriesof copying steps until immediately before the threshold for theemergence of picture image anomalies caused by contaminants in the tonerin the toner recycling unit, based on the acceptable number of count ofcopy sheets, and the prescribed number of count of copy sheets stored inthe prescribed sheet count memory and a cumulative sheet count memory,respectively, and

a selection unit for selectably switching between toner cycling mode andtoner non-cycling mode for the image forming apparatus, based on theacceptable number of count of copy sheets computed by the computingunit.

In addition, this image forming apparatus may further includes a tonerrecycling path unit for transporting the toner removed from the imagebearing member to the developing unit, a toner discarding path unit fortransporting portions of the toner removed by the cleaning unit to atoner discarding tank, and a toner path switching unit for selectablyswitching between the toner recycling path unit and toner discardingpath unit, based on the acceptable number of count of copy sheetscomputed by the computing unit, in which, at the instant when theacceptable number of count of copy sheets is exceeded by the anticipatednumber of count of copy sheets, the toner path switching unit isinstructed to implement the toner discarding mode, in which all of thetoner, that is recovered by the cleaning unit to be recycled into thedeveloping unit, is discarded into a toner discarding tank.

It is noted that the prescribed number of count of copy sheets is thenumber experimentally obtained in advance, under a variety of mutuallyindependent conditions, as the number of count of copy sheets which canbe utilized in image forming for the period of time from the start ofthe recycled use of the toner until immediately before the threshold forthe emergence of picture image anomalies caused by contaminants in thetoner in the toner recycling unit, and that the cumulative sheet countis the number accumulated in the present series of copying steps underrunning conditions as the number of count of copy sheets which isaccumulated in the present series of copying steps after starting therecycled use of said toner, in which the computing unit is adapted tocompute the acceptable number of count of copy sheets which can beutilized in image forming in the forthcoming series of copying stepsunder running conditions until immediately before the threshold for theemergence of picture image anomalies caused by contaminants in the tonerin the toner recycling unit.

Accordingly, it becomes feasible with the present construction of theimage forming apparatus for the toner recovered by the cleaning unit beefficiently recycled without removing contaminants such as aggregatedtoner particles and paper dusts included in the recycled toner, tothereby the emergence of undesirable picture image anomalies beeffectively prevented.

According to still another aspect, an image forming apparatus isdisclosed including at least an image bearing member, an exposure unitfor forming an electrostatic latent image on the image bearing member, adeveloping unit for forming a toner image by developing the latent imageusing toner on the image bearing member, a transfer unit fortransferring the toner image to a substrate, a cleaning unit forcleaning the image bearing member by removing the toner materialremaining on the image bearing member following the transfer, and atoner recycling unit for returning the toner removed from the imagebearing member to the developing unit.

This image forming apparatus is characterized by including the followingadditional units such as

a paper dust measuring unit provided in a paper dust removal unit formeasuring the amount of paper dusts collected in the paper dust removalunit, which are adhered to, and subsequently removed from, feedingrolls,

a dust amount estimating unit for estimating the amount of paper dustsincluded in the toner recovered by the cleaning unit based on theresults from the estimation by the dust amount estimating unit, and

a computing unit for computing the acceptable number of count of copysheets that can be utilized in image forming in the forthcoming seriesof copying steps for the period of time from start of the recycled useof the toner until immediately before the threshold for the emergence ofpicture image anomalies caused by contaminants in the toner in the tonerrecycling unit, based on the results on the amount of paper dusts fromthe estimation by the dust amount estimating unit, and

a selection unit for selectably switching between toner cycling mode andtoner non-cycling mode for the image forming apparatus, based on theacceptable number of count of copy sheets computed by the computingunit.

Accordingly, it becomes feasible with the present construction of theimage forming apparatus for the toner recovered by the cleaning unit beefficiently recycled without removing contaminants such as paper dustsand toner aggregates included in the recycled toner, thereby eliminatingundesirable picture image anomalies.

The present disclosure and features and advantages thereof will be morereadily apparent from the following detailed description and appendedclaims when taken with drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a side view of the copying machine asimage forming apparatus according to one embodiment disclosed herein;

FIG. 2 is a schematic diagram of a side view of the toner recycling unitprovided in the image forming apparatus according to one embodimentdisclosed herein;

FIG. 3 is a schematic diagram of a side view of the toner recycling unitprovided in the image forming apparatus according to another embodimentdisclosed herein;

FIG. 4 includes a flow chart illustrating a process flow for determiningthe timing of switching the modes from toner recycling to non-recyclingaccording to one embodiment disclosed herein;

FIG. 5 contains a graph showing the change in the amount of paper dustsincluded in the toner in the toner hopper with the number of copy sheetsfed during the experimentation;

FIG. 6 contains a graph showing the change in the amount of paper dustsincluded in the toner in the recycled toner with the number of copysheets fed during the experimentation;

FIG. 7 contains a graph showing the change in the amount of paper dustsincluded in the toner with number of copy sheets fed through the modeswitching between toner recycling and non-recycling, in which the graphportions a, c and d correspond to the recycling periods, while theplural portions b correspond to non-recycling period;

FIG. 8 is a schematic diagram of a side view of the toner recycling unitaccording to other embodiment disclosed herein;

FIG. 9 is a schematic diagram of a side view of the toner recycling unitaccording to another embodiment disclosed herein;

FIG. 10 is a schematic view of the shutter device taken from thedirection of the arrow B of FIG. 9;

FIG. 11 includes a flow chart illustrating a process flow forcontrolling the switching mode from toner recycling to non-recyclingaccording to another embodiment disclosed herein;

FIG. 12 includes a graphical plot of experimental results with thenumber of copy sheets fed until the instant when the shutter is switchedto the recycling mode, vertically, versus the number when the amount ofthe paper dusts is reached to that characteristic for the emergence ofthe whisker images, horizontally; and

FIG. 13 illustrates whisker images formed against white background on acopy sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the detailed description which follows, specific embodiments on atoner recycling unit included in an image forming apparatus aredescribed. It is understood, however, that the present disclosure is notlimited to these embodiments, and it is appreciated that the unit andmethod for recycling toner disclosed herein may also be adaptable to anyform of materials recycling. Other embodiments will be apparent to thoseskilled in the art upon reading the following description.

FIG. 1 is a schematic diagram of a side view of the copying machine asimage forming system according to one embodiment disclosed herein. Thecopying machine here is provided with the capabilities such as theelectrophotographic image reproduction and printing. Also, the machinemay additionally provided with the capability as a facsimile unit.

Referring to FIG. 1, the copying machine includes at least aphotoreceptor drum 1 as image bearing member, a charging device 2 foruniformly charging the surface of the photoreceptor 1, an exposure unit30 for forming an electrostatic latent image on the charged surface ofthe photoreceptor drum 1, a developing unit 3 for forming toner imagesusing developing agents D on the photoreceptor 1, a transfer unit 4 fortransferring the developed toner image to a copy sheet P1 (and P2, P3),a fixing unit 40 for fixing the transferred toner image onto the copysheet P1 (and P2, P3), and a cleaning unit 6 for cleaning the surface ofthe photoreceptor 1 by removing residual toner material following thetransfer.

As illustrated in FIG. 1, a document reading unit 50 is provided in theupper portion of main console 100 of the copying machine. A document orimage document (not shown) to be copied is placed on a transparentcontact glass 52 of the document reading unit 50 and illuminated with alight source 53 designed as to be displaced toward the right in FIG. 1.

Being formed by the reflected light, the image of the document isreflected by a multi mirror scanning optics system and then leads to animage pickup device 57. A multi-mirror scanning optics system hereincludes a first mirror 53 movable in coincident with the light source53 and a pair of half rate movable mirrors 55, 56. The optics systemwith the cooperating movable scanning mirrors is a type well known.

The image pickup device 57 is provided with an image sensor such as, forexample, a CCD device (not shown) for inputting the reflected documentimage and a focusing lens (not shown) for focusing the image onto thesensor. The image signals thus input to image pickup device 57 aresubsequently transmitted to the exposure unit 30.

The exposure unit 30 includes at least a rotating polygonal mirror 31for deflecting laser beams L emitted from a laser source (not shown),and mirrors 33, 34, 35 for reflecting the laser beams L which are ledthrough a lens system 32 including an F-θ lens for forming scanningimages.

Subsequently, by exposing the surface of the photoreceptor drum 1 withlaser beams modulated by the image signals previously input to the imagepickup device 57, an electrostatic latent image of the document isformed.

The thus formed electrostatic latent image on the surface of thephotoreceptor 1 is then rendered visible by the developing unit 3through the application of developing material.

The developing unit 3 illustrated in FIG. 1 includes a developer case 16containing a developing agent D and a developing roller 17 rotativelysupported therewithin. Onto the periphery of the developing roll 17, thedeveloping agent D is transported to be utilized for forming visualimages for the latent image.

Although a two-component powder developer, which consists of toner andcarrier, is used as the developing agent D for the developing unit 3 inthe present embodiment, a single- or mono-component developer consistingof toner alone may also be used alternatively.

In addition, the developer case 16 is provided with a toner hopper 3 ain which the toner T is disposed. When the concentration of the toner indeveloping agent D in the developer case 16 decreases, the portion oftoner T in the toner hopper 3 a is supplied by a rotating toner supplyroll 18 to the developer case 16 to be admixed with the developing agentD.

As to copy sheets, ones selected from any of plural stacks of the sheetsP1, P2 and P3 respectively placed in sheet feeding cassettes 61, 62 and63 are fed along the direction of arrow A in FIG. 1 (by way of thepresent example, the cassette P1 is selected). The copy sheet P1 is thenforwarded to the transfer unit 4 in proper registration by aregistration pinch roll pair 5.

The transfer unit 4 includes a transfer belt 4 a which is suspendedwinding around a driving roll 4 b, supporting drive roll 4 c and biasingroll 4 d as illustrated in FIG. 1.

The transfer belt 4 a is formed of such material as to have a mediumrange of electric resistivity in its surface region, and provided forthe movement along the arrow B in FIG. 1 around the above-mentionedrolls 4 b, 4 c and 4 d, to be brought into contact with the surface ofphotoreceptor drum 1 at point S for achieving the image transfer.

In addition, the belt 4 a is also provided such that, on the copy sheetP1 be forwarded past the point S, an electric voltage having thepolarity opposite to that of the toner is applied from a high voltagesource (not shown) to the sheet P1 by way of the biasing roll 4 d.

When this reversed biases voltage is applied to biasing roll 4 d, acurrent flow is caused therefrom to the driving roll 4 b and supportingdrive roll 4 c through the transfer belt 4 a, and further to thephotoreceptor drum 1 through the copy sheet P1. In addition, themagnitude of the applied voltage is adjusted such that the currentthrough the photoreceptor drum 1 stays at a predetermined level suitablefor the transfer current.

Further, the charge generated on the transfer belt 4 a by the biasingroll 4 d during the voltage impression is subsequently discharged by thedriving roll 4 b.

The movement of the copy sheet P1, which is sent out by the registrationpinch roll pair 5 and transported along the transfer belt 4 a, isdesigned to be in proper registration with the toner images on thephotoreceptor drum 1 on passing the aforementioned point S for the imagetransfer.

On passing the point S the toner image on the surface of thephotoreceptor drum 1 is brought in contact with the copy sheet P1 underthe aforementioned voltage, which has the polarity opposite to that ofthe toner and being applied thereon through the biasing roll 4 dprovided on the other side of the transfer belt 4 a. As a result, thetoner image on the photoreceptor drum 1 is electrostatically transferredto the contacting side of the copy sheet P1.

Following transfer of the image, the copy sheet P1, which is forwardedfurther along, and then separated from, the transfer belt 4 a, issubsequently advanced to the fixing unit 40.

The fixing unit 40 includes at least a heated fusing roll pair 40 a, 40b forming a nip between which the copy sheet P1 passes, wherein thetransferred toner image on the sheet P1 permanently fixed.

After fixing the toner image, the copy sheet P1 is advanced to exit niproll pair 70 from where it may be directed to a collecting tray 80.

After transfer some residual toner invariably remains on thephotoreceptor drum 1. The residual toner remaining on the surface of thephotoreceptor drum 1 is removed by the cleaning unit 6.

The cleaning unit 6 includes at least a cleaning case 19, cleaning blade6 a housed within, and disposing screw 6 b provided in the bottom of thecleaning unit 6 for disposing the toner. The cleaning blade 6 a suitablyformed of elastic material such as rubber, for example, is providedalong the axial direction of the photoreceptor drum 1 over the region inwhich the toner image is formed (i.e., the residual toner may remain).In addition, one side of the blade 6 a is fixed onto the wall of thecleaning case 19, while the other side thereof is brought in scrapingcontact with the outer periphery of the photoreceptor drum 1, to therebybe suitably adapted to remove the residual toner.

After cleaning the surface the charge remaining on the surface of thephotoreceptor drum 1 is dissipated by a discharging unit 15 consistingof an appropriate lamp. The photoreceptor drum 1 is thereby initializedin preparation for the next copying cycle.

Thereafter, the entire sequence of the copying process steps is repeatedstarting with the charging step by the charging unit 2 to produceanother copy of the document or image document.

It is noted some portions of the toner adhere to a certain extent ontothe surface of transfer belt 4 a as well, which is caused during thetransfer from the photoreceptor drum 1. Since this toner portion mayadhere to the reversed side of the copy sheet P1, if left as is, therebycausing undesirable stains on the sheet. The toner adhered to thetransfer belt 4 a is therefore appropriately removed by a belt cleaningunit 14.

FIG. 2 is a schematic diagram of a side view of the toner recycling unitprovided in the image forming apparatus according to one embodimentdisclosed herein.

Referring to FIG. 2, the toner recycling unit will be describedhereinbelow. As indicated earlier, the cleaning unit 6 is adapted toremove by scraping the residual toner material while in contact with thesurface of the image bearing member. The thus removed residual toner isthen transported by a transporting screw 6 b in the direction normal tothe face of the drawing FIG. 1, to subsequently be lead to a tonerrecycling unit 10.

The toner recycling unit 10 includes at least a toner transporting means11 for selectively transporting the toner material recovered from thecleaning unit 6 to either the developing unit 3 or a toner recoverycontainer 7, and a driving means 12 for driving the toner transportingmeans 11.

The toner transporting means 11 includes at least a transporting pipe 11a provided rotatively along the axis thereof extending in an ascendingmanner from the position capable of receiving the recovered tonertransported by a toner transporting screw 6 b to the toner recoverycontainer 7 by way of the developing unit 3, and a transporting screw 11b provided rotatively in the transporting pipe 11 a for raising thetoner along in the axis direction by rotating the screw 11 a.

The driving means 12 includes a transporting pipe driver 12 including amotor 12 a for rotating the transporting pipe 11 a around the axisthereof in a predetermined direction of the rotation and a gear 12 b tobe engaged with the motor 12 a, and a motor (not shown) for rotating thetransporting screw 11 b.

The transporting pipe 11 a is devised to have an opening 11 a′ situatedat the location connectable to an opposing opening provided on the sideof a toner hopper 3 a of the developing unit 3.

As a result, when the opening 11 a′ is positioned to direct downward asshown in FIG. 1, the toner in the transporting pipe 11 a disposeddownward into the toner hopper 3 a through the adjoining openings, tothereby be rendered to the recycling use (hereinafter referred to asrecycling mode). In contrast, when the transporting pipe 11 a rotates soas the opening 11 a′ to be positioned directing upward as shown in FIG.3, the toner stay in the transporting pipe 11 a to further betransported to the recovery container 7 to be subsequently discarded(non-recycling mode).

The selection of the toner recycling and non-recycling modes thereforebecomes feasible, and the selection or switching between the modes canbe carried out, for example, by a selection switch (not shown) providedin an operation unit.

Namely, in order to carry out appropriate switching steps, the angle ofrotation around the axis of the transporting pipe 11 a is adjusted suchthat the opening 11 a′ selectively directs either downward as shown inFIG. 1 (for toner recycling mode) or upward as shown in FIG. 3 (fornon-recycling mode). This is achieved in practice by devising forcontrol signals be output to the transporting pipe driver 12 from acontrol unit including a CPU (not shown) for suitably carrying out theswitching steps.

The toner recycling unit disclosed herein is characterized by providinga mechanism to determine the timing of switching between the tonerrecycling and non-recycling modes, which is implemented by measuring theamount, and rate of generation, of paper dusts by a paper dust removalunit 20.

That is, on feeding a copy sheet into the position appropriate to imagetransfer in the developing unit, a register unit 5 consisting of aregistration roll pair is adapted to coincide the position of a copysheet with that of toner image on the image bearing member 1. This isachieved with the registration roll pair by bringing the copy sheettemporarily on hold and then forwarded to the proper copying position.

It should be noted that, during paper handling and feeding steps on theupstream of registration rolls, copy papers are subjected to thefriction with several rolls in the feeding path and tend to generatepaper dusts with relative ease. To prevent the paper dusts from enteringinto the area of the image bearing member as much as possible, the paperdust removal unit 20 is provided in contact with at least one of theregistration rolls.

Accordingly, the paper dust removal unit 20 is devised to include atleast a casing 20 a for receiving paper dusts, a blade 20 b for scrapingpaper dusts off from the surface of the registration roll, and aphotosensor 20 c for detecting the amount of paper dusts deposited.

The photosensor 20 c consists of, for example, an optical device ofpaired transmission type light emitter and detector. A plurality of thephotosensors are provided facing one another on opposing inner faces ofthe casing 20 a, to be utilized for detecting the level of the paperdust. Detected signals output from the photosensors are transmitted to,and subsequently processed by, a control unit (not shown).

The paper dust removal unit 20 has been found effective to some extentfor preventing paper dusts from the image bearing member. For example,there prevented by the removal unit are image anomalies such as tonerdeficient streaks caused by the failure in cleaning, that is, by paperdusts clogged between the cleaning blade and image bearing member.

Utilizing the toner recycling unit 20 described above, the timing ofswitching between the toner recycling and non-recycling modes can bedetermined for the image forming apparatus disclosed herein. This isachieved with the photosensor 20 c incorporated into the recycling unit20 by measuring the amount, and rate of generation, of paper dusts inthe casing 20 a. To be more specific, starting from the time zero ofclearing the casing 20 a when the dust amount is also zero, the amountof paper dusts deposited in the casing 20 a is measured over the periodof time when a predetermined number of copied is made.

From the amount of the dust measured and the count of copies made, it isfeasible to determine, among others, the kind or nature of the copysheets currently used such as generating more dusts or having largersizes with less amount of the dusts. Based on these measurements itbecomes also feasible to determine the timing of switching between thetoner recycling and non-recycling modes.

As a result, toner recycling including undue amount of paper dusts canbe alleviated, since the switching between the toner recycling andnon-recycling modes can be properly carried out based on the amount ofthe paper dusts actually measured.

FIG. 4 includes a flow chart illustrating a process flow for determiningthe timing of switching modes from toner recycling to non-recyclingaccording to one embodiment disclosed herein.

Referring to FIG. 4, the process begins in Step 1 where a new tonerrecycling mode is initiated by rotating the transporting pipe 11 aaround the axis thereof such that the opening 11 a′ directs downward asshown in FIG. 1.

The process then proceeds to Step 2, where measurements are carried outto obtain the number count of current copy sheets which tend to generatemore dusts (e.g., recycled paper sheets) currently fed. If the numbercount reaches a predetermined value (YES, in Step 2), the addition ofthe paper size is calculated for all the copies made from the time whenrecycling mode is initiated. The result obtained from the calculation,or hereinafter referred to as cumulative paper size, is subsequentlystored into the control unit.

In Step 3, an inquiry is made regarding whether the thus obtainedcumulative paper size reach a predetermined value stored in advance. Ifthe answer is affirmative (YES), the process proceeds to switch to thenon-recycling mode.

As to the determination of number count of current copy sheets in Step2, the count can be secured by providing a sheet supply unit having withthe following construction. For example, the sheet supply unit has aplurality of shelves, each carrying a different kind of copy sheets suchas recycled, high quality ones, etc. Further, by presetting the shelveseach to respective kinds of the papers and by counting the number ofpapers supplied by respective shelves, the count of copy sheets can beobtained.

With this construction of the sheet supply unit, the number count ofcopy sheets actually supplied during the Steps 1 and 2 can be determinedmore accurately. Accordingly, it can be determined in Step 2 whether thenumber count reaches the predetermined value based on the numberdetermined as above.

The above-mentioned predetermined value, or hereinafter referred to asprescribed sheet count, may be preset based on the results from theexperiments which are carried out in advance with conventional copysheets to obtain the frequency, and the rate of the occurrence ofwhisker images.

The experiments were carried out by the present inventors, and thefollowing results were obtained as illustrated in FIGS. 5 and 6. Namely,FIG. 5 contains a graph showing the change in the amount of paper dustsincluded in the toner in toner hopper 3 a with number of copy sheets fedduring the experimentation. Similarly, FIG. 6 contains a graph showingthe change in the amount of paper dusts included in the toner in therecycled toner with number of copy sheets fed.

It should be noted that the preset value may deviate from the current,actual value depending on detailed running conditions. This deviationmay be reduced by incorporating additional capability of variablysetting the predetermined value into the sheet supply and control units.The predetermined value may therefore be made adjustable with thiscapability depending not only on specific requirements on the whiskerimages by respective users, but also on more detailed control of theamount of toner consumption taking the occurrence of whisker image intoconsideration together with the change in environmental conditions orthe use of special copy sheets.

As to the cumulative sheet count aforementioned in Step 3, its value maybe obtained from the experiments and stored into the control unit as thepredetermined value. In addition, the predetermined value may also bemade adjustable depending on more detailed running conditions and theemergence of whisker images.

The period of time for implementing the toner non-recycling mode isdetermined based on the period for the toner materials be transportedalong the transporting path including through the transporting pipe 11 aand into toner recovery container 7, which is a function of the overalllength of the path and the velocity of the transport.

The period of the non-recycling mode can therefore be obtained ingeneral from the experiments and stored into the control unit as thepredetermined value, to subsequently be utilized for implementing thenon-recycling mode. In addition, the period may also be made adjustabledepending on more detailed running conditions.

FIG. 7 contains a graph showing the change in the amount of paper dustsincluded in toner with number of copy sheets fed through the modeswitching between the toner recycling and non-recycling, in which thegraph portions a, c and d correspond to the recycling periods, while theplural portions b correspond to non-recycling period.

Clearly shown in FIG. 7 is the difference in the pattern of the changesin the dust amount in the toner. Namely, a wavy increase in the graphportion ‘a’ when copy sheets of several different kinds and sizes areused, a rapid and exponential increase in ‘c’ portion when only one kindof, but dusty paper sheets are used, and a relatively slow and steadyincrease in ‘d’ portion when less dusty papers are used.

FIGS. 8 and 9 are schematic diagrams of side views of the tonerrecycling unit 10 provided in the image forming apparatus according tofurther embodiments disclosed herein.

The toner recycling unit 10 is provided with at least one tonertransporting path in which the toner material, which recovered fromphotoreceptor drum 1 by cleaning unit 6 and transported by the disposingscrew 6 b, is transported either to the toner hopper 3 a or the tonerdisposal container 7, and the other transporting path in which theresidual toner, which is removed by the belt cleaning unit 14 from thetransfer belt 4 a, is transported to the toner recovery container 7.

In addition, the selection of the toner recycling and non-recyclingmodes is devised to be appropriately carried out by a shutter 22provided in conjunction with the opening portion 11 a′ of transportingpipe 11 a as shown in FIG. 9. The shutter 22 here is mounted beingpivotably supported by a spindle 23 as shown in FIG. 10 and can berotated by a solenoid 24 around the spindle axis.

With the present construction and in the operating configuration of theshutter 22 indicated by the solid lines in FIG. 10, the toner materialrecovered from photoreceptor drum 1 is transported to the toner disposalcontainer 7 in the non-recycling mode. In contrast, the recovered tonerin the recycling mode is transported to the toner hopper 3 a with theshutter in the operating configuration (or in the retreated position)indicated by the broken lines.

FIG. 11 includes a flow chart illustrating a process flow forcontrolling the switching mode from toner recycling to non-recyclingaccording to another embodiment disclosed herein.

In the present method for controlling the switching mode, severalparameters and the relation therebetween necessary for the control areobtained in advance from the experiments. One of the parameters is thenumber of copy sheets fed up to the instant when amount of the paperdusts is reached to that characteristic for the emergence of the whiskerimages, x(in gram), corresponding to the aforementioned predeterminedvalue of the paper dusts. Another number of copy sheets is then obtainedas that fed up to the instant when the shutter 22 is switched to therecycling mode.

Subsequently, also from experiment, the relation between these two sheetnumbers is obtained. The results from the experiment are shown in FIG.12 which plots the latter sheet number, vertically, versus the formersheet number, horizontally.

Referring again to FIG. 11, the process steps for controlling theswitching mode from of toner recycling to non-recycling are carried outas follows.

The process begins in Step 1 where the shutter 22 is turned OFF (in theaforementioned retreated position) and a new toner recycling mode isinitiated (ON). The process then proceeds to Step 2, where the numbercount for copy sheets fed in the recycling mode is made. In Step 3, aninquiry is made regarding whether the amount of paper dusts recoveredfrom the registration roll reaches the predetermined value of x(g).

Subsequently in Step 4, based on the answer to the inquiry and thegraphical plot in FIG. 12, the amount of paper dusts in recycled toneris estimated. In Step 5, another inquiry is then made regarding whetherthe thus estimated paper dust value reaches the level for switching theshutter 22. If the answer is affirmative (YES), the process proceeds toStep 6 to switch the shutter ON to turn off the recycling mode and toinitiate the non-recycling mode. Next in Step 7, the number count forcopy sheets fed in the non-recycling mode is made.

In Step 8, still another inquiry is made regarding whether the thus madenumber count reaches a predetermined value which is defined by thenumber of copy sheets to be fed during the period of time in which thetoner be transported through the entire path of the recycling unit 10.The predetermined value is therefore a function of the path length forthe toner recycling. If the answer is affirmative (YES), the processproceeds to Step 9 to clear several counts made in the above steps, andsubsequently to Step 10 to switch the shutter OFF, or to turn therecycling mode on.

Since the capability of switching between the toner recycling andnon-recycling modes is provided in the image forming apparatus disclosedherein, process steps suitable for forming the images can be carried outto meet the changes in paper dust actually measured as mentioned above.

That is, by appropriately switching between the toner recycling andnon-recycling modes based on the amount of paper dusts experimentallyobtained, undesirable toner transport to the developing unit 3 can bealleviated, which includes excess amounts of paper dust to cause theaforementioned picture image anomaly such as whisker images.

Although the paper dusts are primarily described with respect to theexcess amounts thereof in the present embodiments, the measurements maybe made also on toner aggregates, to thereby effect the switchingbetween the recycling and non-recycling modes based on the results fromthe toner aggregate measurements, as well.

The apparatuses and process steps set forth in the present descriptionmay therefore be implemented using suitable host computers and terminalsincorporating appropriate processors programmed according to theteachings disclosed herein, as will be appreciated to those skilled inthe relevant arts.

Therefore, the present disclosure also includes a computer-based productwhich may be hosted on a storage medium and include instructions whichcan be used to program a processor to perform a process in accordancewith the present disclosure. The storage medium can include, but is notlimited to, any type of disk including floppy disks, optical disks,CD-ROMS, magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMS, flashmemory, magnetic or optical cards, or any type of media suitable forstoring electronic instructions.

It is apparent from the above description including the examples, themethods and apparatuses disclosed herein for forming electrophotographicimages have several advantages over similar methods previously known.

That is, the image forming apparatus disclosed herein incorporate animproved toner recycling unit. This recycling unit is devised such thatthe selection between the toner recycling and non-recycling modes becontinually carried out according to the decision based on the presentamount of paper dusts measured by the paper dust measuring unit providedin the paper dust removal unit.

The present image forming apparatus incorporating the toner recyclingunit is therefore capable of efficiently recycling the toner recoveredfrom the cleaning unit without removing contaminants such as paper dustsand toner aggregates included in the recycled toner, to thereby be ableto prevent the emergence of undesirable picture image anomalies such aswhisker images and black dots.

Obviously, additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

This document claims priority and contains subject matter related toJapanese Patent Applications No. 2000-363820 and 2001-324641, filed withthe Japanese Patent Office on Nov. 29, 2000 and Oct. 23, 2001,respectively, the entire contents of which are hereby incorporated byreference.

What is claimed as new and desired to be secured by letters patent ofthe United States is:
 1. An image forming method including at least thesteps of forming an electrostatic latent image on an image bearingmember, forming a toner image by developing said latent image usingtoner on said image bearing member, transferring said toner image to asubstrate, and recovering said toner remaining on said image bearingmember following the transfer, comprising the step of: computing anacceptable number of count of copy sheets that can be utilized in imageforming in a forthcoming series of copying steps until immediatelybefore a threshold for the emergence of picture image anomalies causedby contaminants in said toner in said toner recycling unit, based on aprescribed number of count of copy sheets that is experimentallyobtained in advance, under a variety of mutually independent conditions,as a number of count of copy sheets that can be utilized in imageforming for a period of time from start of a recycled use of said toneruntil immediately before a threshold for the emergence of picture imageanomalies caused by contaminants in said toner in said toner recyclingunit, and on a cumulative sheet count which is accumulated, in a presentseries of copying steps under running conditions, as a number of countof copy sheets that is accumulated in said present series of copyingsteps after starting a recycled use of said toner; wherein, if saidacceptable number of count of copy sheets is equal to, or greater thanan anticipated number of count of copy sheets that can be utilized inimage forming in a forthcoming series of copying steps, said forthcomingseries of copying steps are carried out in said toner recycling mode,and wherein, if said acceptable number of count of copy sheets is lessthan an anticipated number of count of copy sheets that can be utilizedin image forming in a forthcoming series of copying steps, saidforthcoming series of copying steps are carried out in said tonernon-recycling mode.
 2. The method according to claim 1, wherein, at aninstant when said acceptable count number of copy sheets is exceeded bysaid anticipated count number of copy sheets, a toner discarding mode isimplemented, in which all of said toner that is recovered by saidcleaning unit to be recycled into said developing unit is discarded intoa toner discarding tank.
 3. An image forming apparatus for use with atleast an image bearing member, an exposure unit configured to form anelectrostatic latent image on said image bearing member, a developingunit configured to form a toner image by developing said latent imageusing toner on said image bearing member, a transfer unit configured totransfer said toner image to a substrate, a cleaning unit configured toclean said image bearing member by removing said toner materialremaining on said image bearing member following the transfer, and atoner recycling unit configured to return said toner removed from saidimage bearing member to said developing unit, comprising: a prescribedsheet count memory configured to store a prescribed count number of copysheets that is experimentally obtained as a count that can be utilizedin image forming for a period of time from a start of a recycled use ofsaid toner until immediately before a threshold for emergence of pictureimage anomalies caused by contaminants in said toner in said tonerrecycling unit; a cumulative sheet count memory configured to store acumulative count number of copy sheets that is accumulated in a presentseries of copying operations after starting the recycled use of saidtoner; a computing unit configured to compute an acceptable count numberof copy sheets that can be utilized in image forming in a forthcomingseries of copying operations under running conditions until immediatelybefore said threshold for the emergence of picture image anomaliescaused by contaminants in said toner in said toner recycling unit, basedon said acceptable count number of copy sheets, and said prescribedcount number of copy sheets, stored in said prescribed sheet countmemory and cumulative sheet count memory, respectively; and a selectionunit configured to selectably switch between a toner recycling mode anda toner non-recycling mode for said image forming apparatus, based onsaid acceptable count number of copy sheets computed by said computingunit.
 4. The image forming apparatus according to claim 3, furthercomprising: a toner recycling path unit for transporting said tonerremoved from said image bearing member to said developing unit; a tonerdiscarding path unit for transporting portions of said toner removed bysaid cleaning unit to a toner discarding tank; and a toner pathswitching unit for selectably switching between said toner recyclingpath unit and toner discarding path unit, based on said acceptablenumber of count of copy sheets computed by said computing unit, wherein,at an instant when said acceptable number of count of copy sheets isexceeded by an anticipated number of count of copy sheets, said tonerpath switching unit is instructed to implement said toner discardingmode, in which all of said toner, that is recovered by said cleaningunit to be recycled into said developing unit, is discarded into a tonerdiscarding tank.
 5. The image forming apparatus according to claim 3,wherein said prescribed count number of copy sheets is a numberexperimentally obtained in advance as said count number of copy sheetsthat can be utilized in image forming for a period of time from thestart of said recycled use of said toner until immediately before saidthreshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling unit, said cumulativesheet count being a number accumulated in said present series of copyingoperations under running conditions as said count number of copy sheetsthat is accumulated in said present series of copying operations afterstarting said recycled use of said toner, wherein said computing unit isconfigured to compute said acceptable count number of copy sheets thatcan be utilized in image forming in a forthcoming series of copyingoperations under running conditions until immediately before saidthreshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling unit.
 6. An imageforming apparatus for use with at least an image bearing member, anexposure unit configured to form an electrostatic latent image on saidimage bearing member, a developing unit configured to form a toner imageby developing said latent image using toner on said image bearingmember, a transfer unit for transferring said toner image to asubstrate, a cleaning unit configured to clean said image bearing memberby removing said toner material remaining on said image bearing memberfollowing the transfer, and a toner recycling unit configured to returnsaid toner removed from said image bearing member to said developingunit, comprising: a paper dust measuring unit provided in a paper dustremoval unit and configured to measure an amount of paper dust collectedin said paper dust removal unit; a dust amount estimating unitconfigured to estimate an amount of paper dust included in said tonerrecovered by said cleaning unit based on results from an estimation; anda computing unit configured to compute an acceptable count number ofcopy sheets that can be utilized in image forming in a forthcomingseries of copying operations for a period of time from a start of arecycled use of said toner until immediately before a threshold foremergence of picture image anomalies caused by contaminants in saidtoner in said toner recycling unit, based on said results on theestimated amount of paper dust by said dust amount estimating unit; anda selection unit configured to selectably switch between a tonerrecycling mode and a toner non-recycling mode for said image formingapparatus, based on said acceptable count number of copy sheets computedby said computing unit.
 7. An image forming means for use with at leastimage bearing means, exposure means for forming an electrostatic latentimage on said image bearing means, developing means for forming a tonerimage by developing said latent image using toner on said image bearingmeans, transfer means for transferring said toner image to a substrate,cleaning means for cleaning said image bearing means by removing saidtoner remaining on said image bearing means following the transfer, andtoner recycling means for returning said toner removed from said imagebearing means to said developing means, comprising: prescribed sheetcount memory means for storing a prescribed count number of copy sheetsthat is experimentally obtained as a count that can be utilized in imageforming for a period of time from a start of a recycled use of saidtoner until immediately before a threshold for emergence of pictureimage anomalies caused by contaminants in said toner in said tonerrecycling means; cumulative sheet count memory means for storing acumulative count number of copy sheets that is accumulated in a presentseries of copying operations after starting a recycled use of saidtoner; computing means for computing an acceptable count number of copysheets that can be utilized in image forming in a forthcoming series ofcopying operations under running conditions until immediately beforesaid threshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling means, based on saidacceptable count number of copy sheets, and said prescribed count numberof copy sheets, stored in said prescribed sheet count memory means and acumulative sheet count memory means, respectively; and selection meansfor selectably switching between a toner recycling mode and a tonernon-recycling mode for said image forming means, based on saidacceptable count number of copy sheets computed by said computing means.8. The image forming means according to claim 7, further comprising:toner recycling path means for transporting said toner removed from saidimage bearing means to said developing means; toner discarding pathmeans for transporting portions of said toner removed by said cleaningmeans to a toner discarding tank means; and toner path switching meansfor selectably switching between said toner recycling path means andtoner discarding path means, based on said acceptable number of count ofcopy sheets computed by said computing means, wherein, at an instantwhen said acceptable number of count of copy sheets is exceeded by ananticipated number of count of copy sheets, said toner path switchingmeans is instructed to implement said toner discarding mode, in whichall of said toner, that is recovered by said cleaning means to berecycled into said developing means, is discarded into a tonerdiscarding tank means.
 9. The image forming means according to claim 7,wherein said prescribed count number of copy sheets is a numberexperimentally obtained in advance as said count number of copy sheetsthat can be utilized in image forming for a period of time from a startof said recycled use of said toner until immediately before saidthreshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling means, saidcumulative sheet count being a number accumulated in said present seriesof copying operations under running conditions as said count number ofcopy sheets that is accumulated in said present series of copyingoperations after starting said recycled use of said toner, wherein saidcomputing means is adapted to compute said acceptable count number ofcopy sheets that can be utilized in image forming in a forthcomingseries of copying operation under running conditions until immediatelybefore said threshold for the emergence of picture image anomaliescaused by contaminants in said toner in said toner recycling means. 10.An image forming means for use with at least image bearing means,exposure means for forming an electrostatic latent image on said imagebearing means, developing means for forming a toner image by developingsaid latent image using toner on said image bearing means, transfermeans for transferring said toner image to a substrate, cleaning meansfor cleaning said image bearing means by removing said toner materialremaining on said image bearing means following the transfer, and tonerrecycling means for returning said toner removed from said image bearingmeans to said developing means, further comprising: paper dust measuringmeans provided in a paper dust removal means for measuring an amount ofpaper dust collected in said paper dust removal means; dust amountestimating means for estimating an amount of paper dust included in saidtoner recovered by said cleaning means based on an estimation; computingmeans for computing an acceptable count number of copy sheets that canbe utilized in image forming in a forthcoming series of copyingoperations for a period of time from a start of a recycled use of saidtoner until immediately before a threshold for emergence of pictureimage anomalies caused by contaminants in said toner in said tonerrecycling means, based on results on the estimated amount of paper dustby said dust amount estimating means; and selection means for selectablyswitching between a toner recycling mode and toner non-recycling modefor said image forming means, based on said acceptable count number ofcopy sheets computed by said computing means.
 11. An image formingmethod comprising: forming an electrostatic latent image on an imagebearing member; forming a toner image by developing said latent imageusing toner on said image bearing member; transferring said toner imageto a substrate; recovering said toner remaining on said image bearingmember following the transfer; and computing an acceptable count numberof copy sheets that can be utilized in image forming in a forthcomingseries of copying operations until immediately before a threshold foremergence of picture image anomalies caused by contaminants in saidtoner in said toner recycling unit, based on a prescribed count numberof copy sheets that is experimentally obtained in advance as a countnumber of copy sheets that can be utilized in forming for a period oftime from a start of a recycled use of said toner until immediatelybefore said threshold for the emergence of picture image anomaliescaused by contaminants in said toner in said toner recycling unit, andon a cumulative sheet count accumulated, in a present series of copyingoperations under running conditions, as a count number of copy sheetsthat is accumulated in said present series of copying operations afterstarting the recycled use of said toner; wherein, if said acceptablecount number of copy sheets is equal to or greater than an anticipatedcount number of copy sheets that can be utilized in image forming insaid forthcoming series of copying operations, said forthcoming seriesof copying operations are carried out in a toner recycling mode, andwherein, if said acceptable count number of copy sheets is less thansaid anticipated count number of copy sheets that can be utilized inimage forming in said forthcoming series of copying operations, saidforthcoming series of copying operations are carried out in a tonernon-recycling mode.
 12. The method according to claim 11, wherein, at aninstant when said acceptable count number of copy sheets is exceeded bysaid anticipated count number of copy sheets, a toner discarding mode isimplemented, in which all of said toner that is recovered by saidcleaning unit to be recycled into said developing unit is discarded intoa toner discarding tank.
 13. An image forming apparatus comprising: atleast an image bearing member; an exposure unit configured to form anelectrostatic latent image on said image bearing member; a developingunit configured to form a toner image by developing said latent imageusing toner on said image bearing member; a transfer unit configured totransfer said toner image to a substrate; a cleaning unit configured toclean said image bearing member by removing said toner materialremaining on said image bearing member following the transfer; a tonerrecycling unit configured to return said toner removed from said imagebearing member to said developing unit; a prescribed sheet count memoryconfigured to store a prescribed count number of copy sheets that isexperimentally obtained as a count that can be utilized in image formingfor a period of time from a start of a recycled use of said toner untilimmediately before a threshold for emergence of picture image anomaliescaused by contaminants in said toner in said toner recycling unit; acumulative sheet count memory configured to store a cumulative countnumber of copy sheets that is accumulated in a present series of copyingoperations after starting the recycled use of said toner; a computingunit configured to compute an acceptable count number of copy sheetsthat can be utilized in image forming in a forthcoming series of copyingoperations under running conditions until immediately before saidthreshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling unit, based on saidacceptable count number of copy sheets, and said prescribed count numberof copy sheets, stored in said prescribed sheet count memory andcumulative sheet count memory, respectively; and a selection unitconfigured to selectably switch between a toner recycling mode and atoner non-recycling mode for said image forming apparatus, based on saidacceptable count number of copy sheets computed by said computing unit.14. The image forming apparatus according to claim 13, furthercomprising: a toner recycling path unit configured to transport saidtoner removed from said image bearing member to said developing unit; atoner discarding path unit configured to transport portions of saidtoner removed by said cleaning unit to a toner discarding tank; and atoner path switching unit configured to selectably switch between saidtoner recycling path unit and toner discarding path unit, based on saidacceptable count number of copy sheets computed by said computing unit,wherein, when said acceptable count number of copy sheets is exceeded byan anticipated count number of copy sheets, said toner path switchingunit is configured to implement said toner discarding mode, in which allof said toner that is recovered by said cleaning unit to be recycledinto said developing unit is discarded into a toner discarding tank. 15.The image forming apparatus according to claim 13, wherein saidprescribed count number of copy sheets is a number experimentallyobtained in advance as said count number of copy sheets that can beutilized in image forming for a period of time from the start of saidrecycled use of said toner until immediately before said threshold forthe emergence of picture image anomalies caused by contaminants in saidtoner in said toner recycling unit, said cumulative sheet count being anumber accumulated in said present series of copying operations underrunning conditions as said count number of copy sheets that isaccumulated in said present series of copying operations after startingsaid recycled use of said toner, wherein said computing unit isconfigured to compute said acceptable count number of copy sheets thatcan be utilized in image forming in a forthcoming series of copyingoperations under running conditions until immediately before saidthreshold for the emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling unit.
 16. An imageforming apparatus comprising: at least an image bearing member; anexposure unit configured to form an electrostatic latent image on saidimage bearing member; a developing unit configured to form a toner imageby developing said latent image using toner on said image bearingmember; a transfer unit for transferring said toner image to asubstrate; a cleaning unit configured to clean said image bearing memberby removing said toner material remaining on said image bearing memberfollowing the transfer; a toner recycling unit configured to return saidtoner removed from said image bearing member to said developing unit; apaper dust measuring unit provided in a paper dust removal unit andconfigured to measure an amount of paper dust collected in said paperdust removal unit; a dust amount estimating unit configured to estimatean amount of paper dust included in said toner recovered by saidcleaning unit based on results from an estimation; and a computing unitconfigured to compute an acceptable count number of copy sheets that canbe utilized in image forming in a forthcoming series of copyingoperations for a period of time from a start of a recycled use of saidtoner until immediately before a threshold for emergence of pictureimage anomalies caused by contaminants in said toner in said tonerrecycling unit, based on said results on the estimated amount of paperdust by said dust amount estimating unit; and a selection unitconfigured to selectably switch between a toner recycling mode and atoner non-recycling mode for said image forming apparatus, based on saidacceptable count number of copy sheets computed by said computing unit.17. An image forming means comprising: at least image bearing means,exposure means for forming an electrostatic latent image on said imagebearing means; developing means for forming a toner image by developingsaid latent image using toner on said image bearing means; transfermeans for transferring said toner image to a substrate; cleaning meansfor cleaning said image bearing means by removing said toner remainingon said image bearing means following the transfer; toner recyclingmeans for returning said toner removed from said image bearing means tosaid developing means; prescribed sheet count memory means for storing aprescribed count number of copy sheets that is experimentally obtainedas a count that can be utilized in image forming for a period of timefrom a start of a recycled use of said toner until immediately before athreshold for emergence of picture image anomalies caused bycontaminants in said toner in said toner recycling means; cumulativesheet count memory means for storing a cumulative count number of copysheets that is accumulated in a present series of copying operationsafter starting a recycled use of said toner; computing means forcomputing an acceptable count number of copy sheets that can be utilizedin image forming in a forthcoming series of copying operations underrunning conditions until immediately before said threshold for theemergence of picture image anomalies caused by contaminants in saidtoner in said toner recycling means, based on said acceptable countnumber of copy sheets, and said prescribed count number of copy sheets,stored in said prescribed sheet count memory means and a cumulativesheet count memory means, respectively; and selection means forselectably switching between a toner recycling mode and a tonernon-recycling mode for said image forming means, based on saidacceptable count number of copy sheets computed by said computing means.18. The image forming means according to claim 17, further comprising:toner recycling path means for transporting said toner removed from saidimage bearing means to said developing means; toner discarding pathmeans for transporting portions of said toner removed by said cleaningmeans to a toner discarding tank means; and toner path switching meansfor selectably switching between said toner recycling path means andtoner discarding path means, based on said acceptable count number ofcopy sheets computed by said computing means, wherein, when saidacceptable count number of copy sheets is exceeded by an anticipatedcount number of copy sheets, said toner path switching means iscontrolled to implement said toner discarding mode, in which all of saidtoner that is recovered by said cleaning means to be recycled into saiddeveloping means is discarded into a toner discarding tank means. 19.The image forming means according to claim 17, wherein said prescribedcount number of copy sheets is a number experimentally obtained inadvance as said count number of copy sheets that can be utilized inimage forming for a period of time from a start of said recycled use ofsaid toner until immediately before said threshold for the emergence ofpicture image anomalies caused by contaminants in said toner in saidtoner recycling means, said cumulative sheet count being a numberaccumulated in said present series of copying operations under runningconditions as said count number of copy sheets that is accumulated insaid present series of copying operations after starting said recycleduse of said toner, wherein said computing means is adapted to computesaid acceptable count number of copy sheets that can be utilized inimage forming in a forthcoming series of copying operation under runningconditions until immediately before said threshold for the emergence ofpicture image anomalies caused by contaminants in said toner in saidtoner recycling means.
 20. An image forming means comprising: at leastimage bearing means; exposure means for forming an electrostatic latentimage on said image bearing means; developing means for forming a tonerimage by developing said latent image using toner on said image bearingmeans; transfer means for transferring said toner image to a substrate;cleaning means for cleaning said image bearing means by removing saidtoner material remaining on said image bearing means following thetransfer; toner recycling means for returning said toner removed fromsaid image bearing means to said developing means; paper dust measuringmeans provided in a paper dust removal means for measuring an amount ofpaper dust collected in said paper dust removal means; dust amountestimating means for estimating an amount of paper dust included in saidtoner recovered by said cleaning means based on an estimation; computingmeans for computing an acceptable count number of copy sheets that canbe utilized in image forming in a forthcoming series of copyingoperations for a period of time from a start of a recycled use of saidtoner until immediately before a threshold for emergence of pictureimage anomalies caused by contaminants in said toner in said tonerrecycling means, based on results on the estimated amount of paper dustby said dust amount estimating means; and selection means for selectablyswitching between a toner recycling mode and toner non-recycling modefor said image forming means, based on said acceptable count number ofcopy sheets computed by said computing means.